Will .Net 4.0 use a new version of the CLR (v2.1, 3.0) or will it stick with the existing v2.0?
Supplementary: Is it possibly going to keep with CLR v2.0 and add DLR v1.0?
Update: Whilst this might look like a speculative question which cannot be answered, the VS team appear to be releasing more and more info on VS10 and .Net 4.0 so this may very soon not be the case. (Info available here -> http://msdn.microsoft.com/en-us/vstudio/products/cc948977.aspx)
4.0 is going to be another side by side release from what I have read.
http://blogs.msdn.com/wenlong/archive/2008/09/07/net-4-0-wf-wcf-and-oslo.aspx
Yes, .NET 4.0 will introduce a new version of the CLR (which will also be at 4.0). The DLR will essentially become a part of the core framework, but it will still sit on top of the CLR.
To state it yet another way - according to Microsoft's Visual Studio 2010 and .NET Framework 4 Training Kit - 4.0 will stand on it's own (i.e., will not sit on top of 2.0 like 3.0 or 3.5 did). Brand new framework and brand new CLR.
As far as the DLR goes it sits on top of the BCL just like Linq, WinForms and WPF does (i.e., DLR -> BCL -> CLR)
To see the PowerPoint slide detailing this click on "Overview" (right-hand side) -> "Lap Around the .NET Framework 4" then click the PowerPoint slide of the same name. Look at the second and third slides.
来源：https://stackoverflow.com/questions/148833/will-net-4-0-include-a-new-clr-or-keep-with-version-2-0